Process for altering the physical properties of finely divided mineral substances



?atented Jan. 12, 1932 UNITED STATES.

PATENT OFFICE RUDOLF ILLNER AN D CAMILLO Fll'RST, OF VIENNA, AUSTRIA; CLARA E'K IBST ADMINIS- TRATRIX OF SAID CAMILLO FllRST, nnonasnn PROCESS FOR. ALTERING THE PHYSICAL PROPERTIES OF FINELY DIVIDED MINERAL SUBSTANCES This invention relates to a process for altering the physical. properties of finely divided mineral substances. Such substances which, in general, are chemically indifferent and find application in various branches of industry, e. g. inpaper making, in the textile industry, or as fillers or colouring matters in the production of rubber goods and artifi cia-l masses freouentl show in soiteof true chemical combination, inadequate physical in a liquid and causing the small particles to "of their components in the liquid in which adsorb one or several slightly soluble substances which are preferably salts. These salts may be formed by double decomposition the mineral substance is suspended.

as is known, finds application in large quan-.

Since one" of the most important of the aforesaid mineral substances is kaolin which titles in the paper and textile industries as fillerand for the purpose of coating in the preparation of shiny types of paper, the inve ei-zplanation, with reference to the treatment of kaolin without being limited thereto.

Kaolin does not always, as may be imagined, prove be suitable for the purposes for which it is to be used, especially if it is required to have fixed properties which are present only the kind of kaolin found in England and known in commerce as china cla should be easily stirrable with water to give perfectly uniform paste and in dilute.

aqueous suspension should have a definite scttlino' velocity, whereby alraolin of pure white tone may be obtained. Moreover, in paper roe ...g, definite behaviour of the kaolin is rec; ired towards the size, casein or the like, v l h which materials certain kaolins are mixed in coating papers. Kaolins which are found in deposits outside England never tron will be described, for the purpose of finch properties are that the kaolin No' Drawing. Application filed October 4, 1928, Serial No; 397,443, and in Austria December 18, 1928.

show the required physical properties, even when their chemical composition agrees with that of English kaolin.

This invention renders it possible to improve" kaolin of any origin so much, that in respect of its physical properties and its bc-- haviour for use in the paper and textile industries it is equal to English china clay. This alteration in the properties of the ordinary lraolinsis obtained according to this invention by suspending them in water and allowing a slightly soluble salt to be adsorbed upon the particles of kaolin. On account of its small solubility in water the adsorbed salt remains adhering to the suspended kaolin particleswhen they are separated from the liquid. It is advantageous, in the practical use of the improved natural product, if the salt concerned is not quite insoluble, for a small. part of the adsorbed salt to go into solution, the charge on the ions resulting in: an electrostatic charge on the solid particles in the medium, which is the cause of the desired physical behaviour observed.

This structure. is attained by the kaolin particles, by the adsorption of comparatively slightly soluble salts, the said salts themselves being formed inan aqueous suspension of kaolin. Any appropriate substances such as acids, bases, salts, may be added to the suspension, which owing to their mutual action, allow a suitable salt to be formed. In choosing the added materials, regard. should be had as to whether the kaolin, after itspurification by an. elutriation process, is to be coagu-Iated in an acid, alkaline or neutral medium. For example, if. a kaolin slurry has been coagulated with milk at lime, its suspension is treated with sulphuric acid until its reaction is neutral. Thereby calcium sulphate is formed, apart of which is: adsorbed upon: the kaolin particles, a part goes into solution, whilst the rest is precipitated. V

A. material may be employed as a reaction component, which inaddition to promoting the above mentioned salt formation, also brings about a bleaching action, e. g. sodium hydrosulphite, whereby the strongly colsulphate by the aforesaid ferric salts.

cured ferric salts are converted into the slightly coloured ferrous salts, these are more easily soluble and remain dissolved,

dized by blowing air or other oxygen-con taining gas through the mixture, the action taking place in the presence of a catalyst, e. g. quite a small quantity of sodium nitrate can be used. Calcium hydroxide is then added until the acid reaction is very slight, I

in order to cause the formation of calcium sulphate. To correct the colour of the purified kaolin a brightening with an insoluble; blue dyestufhsuch as indanthrene or other 1 vat dye, can follow. The addition of these dyestufis may also be made after the addition of the aforesaid reducing agent, which thus reduces and makes them water-soluble, in

which condition the dyestuflf in afinely divided form is adsorbed quite uniformly by the kaolin particles and is regenerated on oxidation of the reducing agent.

The following examples lllustrate how the process of this invention may be carried mto effect 1. A kaolin slurry was obtained from the crude kaolin of an Austrian deposit by meertles of kaolin which conslsts 1n first cochanical elutriation and coagulated by means of milk of lime. This kaolin had a specific gravity of 1.3 and was neutralized in' amixing vessel with sulphuric acid of 60 B.-

Then about 0.1% of powderedsodium hyclrosulphite calculated on the quantity of dry substance present, and double this "weight of sulphuric acid of 60 B. were i for 30-60 minutes.

added, whereupon the mixture was stirred It wasthen neutralized with milk of lime and an'excess of 0.1% of quicklime in the form of milk of lime, reck-' oned on the drykaolin substance, added, and

the mixture again stirred for 30-60 minutes. A ready made, perfectly stable suspension of indanthrene was then added. The quantity of the colouring matter was adjusted according to the desired toneand varied between 7 dried by the application of heat."

0.025% and 0.05% on the kaolin substance. 7 After again stirring for 30 to 60 minutes the slurry was pressed in a filter press and finally 2. A kaolin slurry was obtained from the crude k'aolin'of an Austrian deposit by mechanical elutriation and coagulated with aluminium sulphate. This kaolin had a specific gravity of 1.35and was mixed in a mixing Vessel with 0.1% of hydrosulphite calculated on the dry substance present and an equal quantity of sulphuric acid of 60 Be., whereupon it was stirred for -60 minutes. Then it was neutralized with milk of lime and furwhereupon slaked lime was added until the acid'reaction'was very slight, whereby the soluble ferrous and ferric salts remain in solution. 7

If, after this process, the colour of the kaolin is still not that which is desired, it may be brightened with an organic dyestufi which is fast'to alkali and acid, e. gxan indanthrene dye. The quantity of such dyestuff added, may be adjusted according to the inherent colour of the kaolin and according to the tone to be obtained. 7

By the above described process calcium sulphate is formed. Onthe one hand the adsorption by the kaolin particles is lowered owing to the reduction and solution of the iron particles in the acid whileon the other hand these particles become covered with a white layer and thereby become lighter in colour.

l/Vhat we claim is A process for altering the physical. propagulating crude kaolin with milk of lime,

then neutralizing the same with sulphuric acid of 1%., then adding powdered so dium hydrosulfite in the proportion of about 1 part to 1000 parts of dry kaolin present,

vtogether with about 2 parts of sulfuric acid of 60 B. while stirring the mixture for 30 to 60 minutes; thereupon neutralizing the mixture with milk of lime having an excess of 1 part of quick-lime to 1000 parts of drly kaolin, then again stirring themixture for tures.

RUDOLF ILLNER. OAMILLO FIRST.

about the same length of time; then adding 

